Objectives of this research are to (a) conduct a cross-sectional study of linguistic skills in undocumented carriers and noncarriers of the APOE 4 gene; (b) examine relationships between APOE 4, regional glucose metabolisms, and cognitive abilities; (c) follow participants over three years, and compare groups for cognitive and neurobiological change; and (d) develop a model for the prediction and differential diagnosis of AD. the ability to provide valid predictions and diagnoses will become increasingly critical as prophylactic and therapeutic treatments for AD become available. Oral and written language samples, neuropsychological, PET and MRI data will be acquired. One-factor ANOVAs will be used to compare groups for grammatical complexity and other measures thought to contribute to linguistic adequacy (e.g., number of words, propositions and content units; proposition density type-token ratio; mean length of utterance). Longitudinal data will be analyzed with repeated measures ANOVAs. Relationships between genotype, regional glucose metabolism, and language measures will be examined using the Pearson product moment correlation coefficient. These and other variables associated with APOE 4 and/or AD will be entered into a discriminant function analysis to determine maximum discrimination between groups. A model will then be developed for predicting and diagnosing AD. This research will provide the foundation for a subsequent, more comprehensive study of persons at risk for AD.